One who runs a German out (7)
I believe the answer is:
manager
'one who runs' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a german out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'a'+'german'='agerman'
'agerman' anagrammed gives 'MANAGER'.
Can you help me to learn more?
(Other definitions for manager that I've seen before include "Supervisor" , "suit?" , "One running a shop, industry etc" , "Person in charge of staff" , "Ran game (anag.)" .)